The present invention relates to a servo system for a magnetic disk memory having spiral data tracks.
Generally, a magnetic disk device uses magnetic disks with concentrically formed data tracks. With this type of disk device, a read/write head stays on one track until the head is instructed to access another track. It is relatively easy, therefore, to perform positioning control of the head. Disks having concentrical data tracks are advantageous for easier realization of high-density tracks.
On the other hand, to write (read) a great amount of information, such as image information, on the concentrical tracks of a disk, track access control must be performed many times. Therefore, the writing (reading) of information cannot continuously be performed. A relatively long period of time is required to gain access to tracks, resulting in a substantial reduction in the data transfer rate.
Taking into consideration the disadvantage of concentric-track disks, forming a spiral track on a disk has been proposed. Since, in the case of a spiral track disk, the data track is continuous on the disk, and repeated access to the track is not required in writing and reading image information. This enables continuous writing of information on the disk. Further the data transfer rate is not lowered.
In a conventional disk device with a spiral-track disk, the head is simply moved in the radial direction of the disk. Therefore, it is difficult to move the head to a desired position on a track to write and read information. In other words, the conventional disk device cannot directly access the desired position on the data track. Further, the simple mechanical actuation of the head in the radial direction of disk requires some allowance for head tracking, making it difficul to increase track density.
An improved servo system for a disk having concentric tracks is disclosed in the copending U.S. patent application Ser. No. 469,144, entitled "SYSTEM FOR DETECTING POSITION OF A READ-WRITE HEAD IN SEEK OPERATION ON A DISK MEMORY HAVING DATA AND SERVO SECTORS", filed Feb. 23, 1983, now U.S. Pat. No. 4,499,511, and assigned to the same assignee as this application.
A further improved servo system for a disk having concentric tracks is disclosed in the copending U.S. patent application Ser. No. 586, 440, entitled "SYSTEM FOR DETECTING THE POSITION OF A READ-WRITE HEAD ON A DISK RECORDING MEDIUM HAVING DATA AND SERVO SECTORS", filed Mar. 5, 1984 and assigned to the same assignee as this application.